In combustion systems such as gas turbines, aircraft engines, rocket motors and heating systems, thermoacoustically induced combustion oscillations can occur. These are caused by an interaction of the combustion flame and the associated heat release with acoustic pressure fluctuations. As a result of an acoustic stimulation, the location of the flame, the flame front surface or the mixture composition can fluctuate, thereby causing fluctuations in the heat release. In the case of constructive phase positions, positive feedback and amplification can occur. Such an amplified combustion oscillation can result in significant noise exposure and damage due to vibrations.
These thermoacoustically induced instabilities are greatly influenced by the acoustic properties of the combustion chamber and the marginal conditions which are present at the combustion chamber entrance and combustion chamber exit and at the combustion chamber walls. The acoustic properties can be changed by installing Helmholtz resonators.
WO 93/10401 A1 shows a device for suppressing combustion oscillations in a combustion chamber of a gas turbine installation. A Helmholtz resonator is connected to the flow of a fuel feed line. The acoustic properties of the feed line or of the acoustic overall system are thereby changed in such a way that combustion oscillations are suppressed. However, it is also apparent that this measure is not sufficient in all operating states, since combustion oscillations can still occur when oscillations in the fuel line are suppressed.
U.S. Pat. No. 6,058,709 proposes the introduction of fuel at axially differing positions in the combustion channel of a combustor, in order to avoid combustion oscillations. Consequently, with regard to the development of combustion oscillations, constructive phase positions in the mixture composition are superimposed by destructive phase positions, thereby achieving lower fluctuations overall and therefore a decreased tendency to develop combustion oscillations. In terms of equipment, however, this measure is relatively expensive in comparison with the purely passive measure of using Helmholtz resonators.
EP 0 597 138 A1 describes a gas turbine combustion chamber which features air-flushed Helmholtz resonators in the area of the combustors. Vibrational energy from combustion oscillations which occur in the combustion chamber is absorbed by these resonators, and the combustion oscillations are consequently attenuated.
A further measure for attenuating combustion oscillations is shown in EP 1 004 823 A2. In this case, a Helmholtz resonator is connected directly to the mixing area of the combustor. It is emphasized and explicitly disclosed that the resonator must be attached upstream of the fuel feed, since combustion oscillations deriving from the resonator in the combustor and also combustion oscillations which are caused by the feed lines are to be absorbed.
The invention addresses the problem of specifying a combustor which has a particularly low tendency to develop combustion oscillations. The invention further addresses the problem of specifying a method for operating a combustor, which method efficiently prevents combustion oscillations. Lastly, the invention addresses the problem of specifying a gas turbine which has a particularly low tendency to develop combustion oscillations.